1. Field of the Invention
The present invention relates to a suction pad capable of attracting and transporting a workpiece.
2. Description of the Related Art
A vacuum cup (suction pad) has been hitherto used in order to attract and transport a workpiece under an action of a negative pressure. As shown in FIGS. 11 and 12, the conventional vacuum cup 1 comprises a main cup body 4 including a base section 2 and a skirt section 3 which are integrally formed with a flexible material such as rubber. The skirt section 3 has grooves 6, 7 provided on an attracting surface 5 thereof. The grooves 6 are formed in a circumferential direction of the skirt section 3 and the grooves 7 are formed to intersect the grooves 6 formed in the circumferential direction (see Japanese Laid-Open Patent Publication No. 9-11172).
With the conventional vacuum cup 1, if oil film or water droplet adheres to a surface of an attracted object, the oil film or the water droplet intervening between the skirt section 3 and the surface of the attracted object is wiped away by cutouts constituting the grooves 6 formed in the circumferential direction. The oil film or the water droplet is excluded after it is gathered toward a center of the main cup body 4 by the grooves 7 in a radial direction of the skirt section 3. The radial direction thereof intersects the grooves 6 in the circumferential direction. Accordingly, the vacuum cup 1 is supposed to hold the attracted object against being out of position and falling due to a slip thereof.
However, with the conventional vacuum cup 1, only the grooves 6, 7 formed by the cutouts function as an acting surface under the negative pressure in the skirt section 3 tightly contacting with the attracted object. Therefore, there is a problem that an attracting force under the negative pressure cannot be increased so much.
It is a general object of the present invention to provide a suction pad which can reliably hold a workpiece against falling off without causing a slip thereof by further increasing an attracting force under a negative pressure even if oil film or water droplet adheres to an attracted surface of the workpiece.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.